1. Field of the Invention
The present invention relates to a bidirectional switch, which requires a high breakdown voltage, and a switch circuit using said bidirectional switch.
2. Description of the Related Art
Generally, a switch using a MOSFET (metal-oxide-semiconductor field-effect transistor) is preferably such that a voltage between source and backgate (source-backgate voltage) be constant in order that the impedance does not vary depending on an input level. In order to make the source-backgate voltage constant or fixed, a source terminal and a backgate terminal (hereinafter sometimes referred to as “body terminal” and “bulk terminal”, respectively) are shorted, so that a parasitic diode made by a p-n junction is formed between the source and the drain. Accordingly, in n-channel MOSFETs, the current flows through the parasitic diode from a source side to a drain side in the event that the gate is turned off. As a result, the signal from the source side to the drain side cannot be blocked off.
In view of the above, used is a generally-known method where two MOSFETs are connected in series with each other so that the directions of the parasitic diodes become opposite in order to enable the switching of signals in both directions.
However, in the bidirectional switch inserted into the power supply line that transmits electricity at high voltage, the size of the two MOSFETs must be made larger to improve the high breakdown voltage characteristic. Use of the two large-size MOSFETs increases the total circuit area of the bidirectional switch.